Magnetic bearings are used to levitate and support a rotor in a magnetic field and simultaneously provide stiffness and damping to the rotor. In some applications, especially subsea applications, magnetic bearings are often sealed within a housing or chamber to protect the bearings from external contamination. For example, bearings in subsea applications are constantly threatened by the ingress of sea water or other corrosive fluids that could prove fatal to the bearings if not adequately protected by the housing. Such a sealed bearing is generally known as a “canned” bearing.
The housing of a canned bearing also serves to protect the magnetic bearing from damaging external pressures. To prevent implosion or structural collapse from increased external pressures, the housing is often filled with a “potting material” such as a resin or an epoxy. The potting material fills in the voids around the poles, coils, windings, and instrumentation of the magnetic bearings, such as the position and temperature sensors, and hardens to form a solid structure. The potting material not only provides structural support to the housing to resist pressure escalations, but also acts as an electrical and thermal insulator for the bearings.
One drawback to conventional canned magnetic bearings, however, is the need to replace the entire bearing when an integral component fails. Because the potting material forms a hardened structure all about the magnetic bearing, simple repairs or replacements of bearing components, such as coils or poles, is essentially impossible. Instead, the canned magnetic bearing must be disposed of and replaced with a new bearing. Another drawback to conventional canned magnetic bearings is a poor heat transfer capacity. While magnetic bearings do not generate enormous amounts of heat, it is nonetheless beneficial to remove bearing heat in order to extend the life of the bearing. Canned magnetic bearings with potting material, however, depend heavily on conduction heat transfer which can be relatively inefficient since the heat is required to pass through the insulating potting material before being transferred to the external environment.
What is needed, therefore, is a cooling system for canned magnetic bearings that overcomes the disadvantages described above, and still provides for adequate support for the magnetic bearing.